The present invention relates to a display control apparatus, particularly to a control apparatus for a raster scan type display having a bit map memory and one or more look-up tables.
In many of the raster scan type displays having a bit map memory, a look-up table (also referred to as a video look-up table, a color table or a color map, and hereinafter abbreviated as LUT) is used (for instance, refer to A. Van Dam "Fundamentals of Interactive Computer Graphics" pp. 129-135, Addison - Wesley, 1982). A LUT is a kind of conversion table, and it converts the data read out from a bit map memory as a refresh buffer, using that data as the table index, to the signals for controlling the luminance or color of a CRT. In addition , a system is known in which the data from a bit map memory is directly utilized as the luminance signals or color signals (red, green and blue) for a CRT without passing through a LUT.
In the conventional display, only one or the other of converted display which uses a LUT and direct display which does not use a LUT is selected for the whole of a bit map memory. However, in some cases, it is desirable that converted display which uses a LUT is selected for some area in a bit map memory and direct display which does not use a LUT is selected for the other area. For instance, when an image generated by computer graphics and a landscape image photographed by a camera are superimposed for display, it is convenient that the former image stored in some area in a bit map memory is displayed after the conversion by a LUT and the latter image stored in the other area is directly displayed without using a LUT. Such combination of converted display and direct display on a single screen has many applications, and is expected to contribute to the enrichment of image processing technique. Further, the superimposition of images converted in different ways by different LUTs is also useful.